JPH0467929A - Heating cylinder temperature control method for injection molding machine - Google Patents

Abstract

PURPOSE:To make the temperature variation of a heating cylinder before and after the start of molding small nd shorten the time from starting to the stabilized state by computing preliminarily the amount of heat removed from the heating cylinder by the introduction of resin into the heating cylinder and giving said amount of heat to the heating cylinder simultaneously with the start of molding. CONSTITUTION:A forced heating system 20 comprises a heater 21 installed on a heating cylinder separately from an exhausting band heater a control section 22 for outputting a molding signal at the start of molding,a switch 23 applying power to the auxiliary heater 21 by means of a mold starting signal, a timer 24 for performing the timing action by means of the mold starting signal and outputting a signal for shutting off the power to the auxiliary heater 21 after the given time passed and a switch 25 for shutting off the power to the auxiliary heater 21 by means of a signal from said timer 24. The auxiliary heater 21 is installed on the heating cylinder together with the exhausting band heater in the form of double layer structure, and the heater capacity and the heating time T forming the amount of heat are set therein.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a heating cylinder temperature control method for an injection molding machine.

(Prior Art) A heating cylinder of an injection molding machine is provided with a band heater, and resin supplied from a hopper is heated and melted within the heating cylinder and injected from a nozzle. In order to improve the quality of the molded product, it is preferable that the temperature of the heating cylinder be maintained as constant as possible.

FIG. 4 shows a conventional heating cylinder temperature control system.

In FIG. 4, a temperature detector 42 such as a thermocouple is provided at a predetermined position of a heating cylinder 41, and a detection signal is feedhacked to the input side of the temperature control system. The deviation e between the set temperature θ and the detected temperature is input to the PID controller 43. When the deviation e becomes larger than a predetermined value, the PID controller 43 outputs a control signal that turns on electricity to the band heater 44 provided in the heating cylinder, and turns off the electricity when m and Ie become smaller. Outputs a control signal to

(Problem to be Solved by the Invention) However, with such a temperature control system, as shown in FIG. do not have. This is due to the fact that low-temperature resin is supplied into the heating cylinder from the hopper at the start of molding. Also, the amount of heat removed from the heating cylinder by the introduced resin is large.

The temperature control system cannot follow the temperature sufficiently, and as a result, once the temperature of the heating cylinder drops, it takes a considerable amount of time to restore the temperature.

In view of these problems, an object of the present invention is to shorten the time required for stabilizing the startup of an injection molding machine by compensating for the temperature drop in the heating cylinder caused by the introduction of low-temperature resin. be.

(Means for Solving the Problems) The present invention is characterized by comprising a means for heating a heating cylinder for a predetermined period of time at the start of molding, and this heating means:
an auxiliary heater separate from the heater disposed on the heating cylinder; means for energizing the auxiliary heater in response to a molding start signal; and means for cutting off energization to the auxiliary heater when the predetermined time has elapsed after the start of molding. including.

(Function) The heating means according to the present invention operates in synchronization with the introduction of low-temperature resin, and is used to cover the amount of heat absorbed by the introduced resin.

(Example) An example of the present invention will be described with reference to FIGS. 1 to 3.

In FIG. 1, the heating cylinder temperature control system according to the present invention includes a forced heating system 2 in addition to the control system 10 shown in FIG.
0.

The forced heating system 20 includes an auxiliary heater 21 provided in the heating cylinder separately from the existing band heater.

A control unit 22 that outputs a molding start signal when molding starts, and a switch 23 that energizes the auxiliary heater 21 based on the molding start signal.
In response to the molding start signal, a timer 24 performs a timing operation and outputs a signal to cut off the energization to the auxiliary heater 21 when a predetermined time has elapsed, and the signal from the timer 24 cuts off the energization to the auxiliary heater 21 A switch 25 is included.

As shown in FIG. 2, the auxiliary heater 21 is installed in a heating cylinder in a two-layer structure together with the existing hunt heater, and the heater capacity and heating time T, that is, the amount of heat generated, are set as described below. .

In FIG. 3, the shaded area is the amount of heat taken away because the resin is supplied from the hopper into the heating cylinder.

This heat ff1q is obtained by an octagonal equation.

ql z Amount of heat removed from the cylinder per unit time and unit area [W/I]: Time when it starts to drop from a steady state Time when it returns to a steady state ρ: Specific weight of the heating cylinder [kgf/m3]
C9 Heating cylinder specific heat ■, Heating cylinder volume [m 3 θ.

Temperature of heating cylinder in regular state [°C] θ, 2. Heating cylinder temperature [''CI at a certain time] Next, heat radiation m Q 2 from the heating cylinder surface is determined by the following equation.

q2: Amount of heat dissipated from the heater surface per unit area/unit time CW/I] α, Heat transfer coefficient of the heater surface [W/I°C] θ-: Ambient temperature
From CI1 (1) and (2) equations, the amount of heat in the shaded area q
The heat ff1q required to cover , is determined by a quadratic equation.

The heating time T of the auxiliary heater 21 is determined in advance through experiments as described below, and the auxiliary heater 21 is continuously heated for the time T at the same time as the forming start signal is generated.

This control method operates as follows.

The timer 24 is set with a time T that is roughly calculated using the method described above.

When the injection molding machine is started up and molding starts, the control section 22 outputs a molding start signal to the switch 23 and the timer 24. This closes the switch 23 and starts energizing the auxiliary heater 21.

At the same time, the timer 24 starts counting, and after a predetermined time T, the timer 24 times up and opens the switch 25. In this way,
The auxiliary heater 21 heats the heating cylinder for a time T from the start of molding. Subsequent temperature control is performed by the temperature control system 10.

In addition, in the explanation of the embodiment, the case where the auxiliary heater is provided separately from the band heater has been explained, or the heat generation capacity of the band heater is increased by the capacity of the auxiliary heater, and the voltage,
The amount of heat generated may be controlled by controlling the current.

(Effects of the Invention) As described above, in the single control system, the amount of heat taken away from the heating cylinder by introducing resin into the heating cylinder is calculated in advance, and this amount of heat is given to the heating cylinder at the same time as molding starts, thereby making it possible to form the cylinder. The temperature fluctuation of the heating cylinder before and after the start can be reduced, and the time required to stabilize the start can be shortened.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram for explaining a method of arranging a band heater and an auxiliary heater arranged in a heating cylinder, and FIG. 3 is a diagram showing a configuration of an embodiment of the present invention. FIG. 4 is a diagram for explaining the principle of the control method, FIG. 4 is a diagram showing the configuration of the conventional example, and FIG. 5 is a diagram for explaining the drawbacks of the conventional example. In the figure, 20 is a forced heating system, and 21 is an auxiliary heater. 22 is a control unit, 23.24 is a switch, 25 is a timer 0

Claims (2)

[Claims] (1) In an injection molding machine that has a control system that detects the temperature of a predetermined part of the heating cylinder and controls energization to a heater installed in the heating cylinder based on this detection signal, the heating is performed for a predetermined period of time at the start of molding. A heating cylinder temperature control system for an injection molding machine, characterized by comprising means for heating the cylinder. (2) In the heating cylinder temperature control method according to claim (1), the heating means includes an auxiliary heater other than the heater disposed in the heating cylinder, and energizes the auxiliary heater in response to a molding start signal. 1. A heating cylinder temperature control system for an injection molding machine, comprising: means for cutting off electricity to the auxiliary heater when the predetermined time has elapsed after the start of molding.